A good deal of work has been done to create materials or utensils that permit foods to be cooked in a microwave oven to obtain the cooking characteristics of conventional ovens. The most popular device being used is the plain susceptor material. Plain susceptors are convenient in cooking applications and low in cost.
Susceptors have been widely used in microwave food cooking since the early 1980's. Susceptors can be quite effective in generating local surface heat and contributing significantly to crisping of food surfaces. However susceptors failed to meet the full microwave cooking potential due to three distinct problems.
First, susceptors have an inability to uniformly brown and crisp items in a similar way as conventional ovens. The edge region of a susceptor is generally much hotter compared to the center region of the susceptor. This effect is often caused by the E-field strength in the edge of the plain susceptor being stronger than the center region due to the loading effects of the adjacent foodstuffs.
Secondly, there is the inability to generate uniform temperature distributions within bulk products. This effect is due to the susceptor's inability to conduct power parallel to its surface or to provide good shielding.
Thirdly, the susceptor has an inability to generate consistent heating under varying microwave E-field strengths as well as different loading conditions of the food. Portions of a susceptor that are exposed to high electric field strengths and/or poor heat sinking tend to overheat. This overheating causes thermal damage to the substrate and hence damage to the metallized layer. The net result is that the susceptor becomes substantially transparent.
In general, susceptor material does not have any ability to control non-uniformity and to adapt to the variations of oven field strength and loading applications. In other words, susceptor material has only a limited ability to obtain uniform and reliable heating power within the microwave oven.
Other solutions have proposed the use of different patterned structures, such as square matrixes or "fused" structures, to avoid the over heating of the susceptor edge. Such square matrixes and other shaped structures are described in U.S. Pat. Nos. 5,260,537 and 5,354,973. However these patterned structures lead to significant reduction in the overall power absorption capability of the susceptor material. As a result, such susceptors can only function as a weak surface heating material.